Arsenic is a well-known carcinogen, and arsenic contamination of groundwater is a widespread occurrence affecting vast regions in India, Bangladesh, China, Mexico, Argentina, and the United States. According to World Health Organization (WHO), permissible limit of conc. of arsenic in water is 10 microgram per liter. Permissible limit of arsenic in industrial waste is 10 ppm. In ground water arsenic remains in two water soluble oxidation states, arsenic (III) and arsenic (V) among which Arsenic(III) is more toxic due to its soft nature. Higher conc. of arsenic in regular drinking water may cause several damages like hyperkeratosis, depigmentation, skin cancer, cancer in the lungs, bladder, liver, kidney and prostate. So detection and removal of arsenic from drinking water is very important for human health. Laboratory techniques used to detect arsenic are atomic fluorescence spectroscopy (AFS), graphite furnace atomic absorption (GFAA), inductively coupled plasma emission spectrophotometry (ICP-AES), inductively coupled plasma mass spectroscopy (ICP-MS), hydride generation atomic adsorption (HGAA), atomic absorption spectrometry (AAS) and neutron activation analysis. Although these methods can accurately measure arsenic in an environmental sample to microgram arsenic per liter concentrations, they require tedious sample preparation and pre concentration procedures, expensive instruments, and professional personnel. Moreover, they cannot be used as portable devices for on-site detection.
Article titled “Detection of trace amount of arsenic in groundwater by laser-induced breakdown spectroscopy and adsorption” by A Haider et al. published in Optics & Laser Technology, March 2014, 56, Pages 299-303 reports LIBS technique coupled with adsorption for the efficient detection of arsenic in liquid. Several adsorbents like tea leaves, bamboo slice, charcoal and zinc oxide have been used to enable sensitive detection of arsenic presence in water using LIBS. Arsenic in water at 1 ppm level reported by a combination of LIBS and adsorption by ZnO.
Article titled “Ultrasensitive mercury(II) ion detection by europium(III)-doped cadmium sulfide composite nanoparticles” by H Q Chen et al. published in Talanta, 2010, 83 (1), pp 139-144 reports Eu3+-doped cadmium sulfide composite nanoparticles synthesized through a straightforward one-pot process. The article also reports a process for the detection of trace Hg2+ in aqueous solutions.
US patent application no. 20110220577 discloses a process for the removal of arsenic and Cr(III&VI) from contaminated water using zinc peroxide nanoparticles which comprises treating the contaminated water containing arsenic and chromium with the nanoparticles of zinc peroxide in a ratio (w/v) ranging from 8:1 to 12:1 (mg/ml), having the concentration of arsenic, Cr(III&VI) contamination below 50 ppm in water, at ambient temperature, for a period of 5-10 min, followed by filtration to obtain the desired low concentrated contamination permissible drinking water.
US patent application no. 20060207945 discloses a method for removing arsenic from an aqueous feed which comprises contacting said aqueous feed with solids consisting essentially of a compound containing cerium in the +4 oxidation state to oxidize and remove said arsenic from said feed and thereby produce an aqueous fluid having a reduced arsenic concentration as compared to said aqueous feed, wherein said solids consist essentially of cerium dioxide.
U.S. Pat. No. 6,197,201 discloses a process for removing or stabilizing arsenic and/or selenium from aqueous streams or slurries is provided that includes contacting the streams or slurry with a composition containing lanthanum chloride. The lanthanum chloride composition can optionally contain various lanthanides. These lanthanide series of elements includes the elements lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.
PCT application no. 2012040650 discloses a method for treating water and/or a water handling system with one or more rare earths to decrease deposit formation and/or to remove a deposit, wherein the deposit material can comprise one or more of fluoride, arsenite, arsenate, antimonite, bismuthate, pnictogon and the term “Rare earth” refers to one or more of yttrium, scandium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium erbium, thulium, ytterbium, and lutetium.
Article titled “Removal of arsenite and arsenate ions from aqueous solution by basic yttrium carbonate” by S A Wasay et al. published in Water Research, 1996, 30 (5), pp 1143-1148 reports a new method to remove arsenite and arsenate ions from aquatic systems by using basic yttrium carbonate (BYC). The removal by adsorption of arsenite and arsenate ions was reported to be >99% depending on initial concentration in the pH range of 9.8-10.5 and 7.5-9.0, respectively.
U.S. Pat. No. 7,338,603 discloses a process for removing oxyanions of an element using a sorbent comprising one or more rare earth compounds to remove one or more of said oxyanions, wherein the rare earth compounds are selected from lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium and scandium.
Therefore, a new highly effective, reliable, and economical technique is needed to meet the new lowered arsenic maximum contaminant level. The prior cited references indicated about the detection of Arsenic in water in the range of 1-50 ppm level by a combination of LIBS and adsorption by ZnO, Zinc peroxide, Cerium dioxide, lanthanide chloride, yttrium carbonate, etc. Compared to other known and reported techniques, the present invention of arsenic removal systems using adsorption usually do not take up a large amount of space or require additional chemicals for treatment of the water, and do not generate sludge that must be disposed of.